Support for a self-propelled linear motion drive apparatus

Abstract: The invention supports a mechanical carriage (12) at three contact points for precise positioning on two guide rails (14,16), one guide rail (14) having a V-grooved surface (24) and the other (16) having a flat surface. Two of the three contact points are recirculating ball bearings (22) mounted against the V-grooved rail (14). The third contact point is on the flat rail (16) and is also the driving contact point and comprises a drive shaft (30) having a friction wheel (50) thereon engaged with the flat rail to drive the mechanical carriage (12). The recirculating ball or roller bearings (22) and friction wheel (50) are loaded against the V-grooved (14) and flat (16) rails, respectively, by magnets (60,62,80) mounted on the carriage (12) and spaced from the rails by an air gap (66,68). The air gap provides for a magnetic force between the magnets and the guide rails while permitting relative movement therebetween.

Description: The present invention relates to a support system for a carriage of a linear drive apparatus, and in particular for a self-propelled linear drive apparatus. An example of a support system in a prior art linear drive apparatus is disclosed in US-A-1 746 407, in which light is scanned onto a cylindrical surface by a beam deflector mounted on a rotating shaft inside the cylindrical surface. The cylindrical surface is moved linearly in a slide type of guide relative to the beam deflector mounted on the rotating shaft. This type of support system for the linear drive requires an operating space twice the length of the cylinder, due to the cylinder being driven linearly relative to the beam deflector. Another support system for a carriage of a linear motion drive apparatus is disclosed in GB-A-1 185 115, in which a carriage is moved linearly inside of a cylindrical drum by a rotating threaded rod engaging a nut assembled in the carriage. The carriage is supported by a longitudinal slot in the cylinder parallel to the axis of motion through which the carriage is coupled with the threaded rod by the nut. The threaded rod is rotated by a motor mounted outside of the cylinder. Another embodiment shown in GB-A-1 185 115 uses a belt, connected to the carriage to pull the carriage linearly inside the length of the cylinder. The belt is driven by means of pulleys mounted externally of the cylinder at the two ends of the cylinder. The pulleys are driven by an auxiliary motor. The carriage is supported by guide rollers which are in contact with the inner surface of the cylinder and which center the axis of linear motion with the axis of the cylinder. A longitudinal guide is provided to prevent the carriage from rotating relative to the cylinder. Both of the embodiments have motors and other elements of the drive systems mounted externally of the cylinder requiring valuable space within the imaging system. In US-A-4 816 847, two slidable members are driven along a guide and a flat rail by drive bands which are moved by friction motors. Each driven slidable member is supported in three points. The first two points of slidable contact are co-aligned and engaged with the guide, and the third point of slidable contact is on the flat rail. Two C-shaped recirculating ball bearings slide along the guide while a set of opposed rollers engage the flat rail on opposing sides of the flat rail. Drive band systems and belt and pulley systems of linear motion apparatus require numerous elements such as a lengthy drive bands and belts, tensional mechanisms, and support components for members being driven by such systems. The number of elements and size and cost of such an apparatus is greatly reduced by incorporating a drive element into the support system, thereby providing a support for a self-propelled linear motion apparatus. Another example of a prior art system can be found in US-A-4 909 093. That patent discloses a friction drive mechanism for a motorized sliding door. The door is suspended on only one stationary supporting elongate guide rail, and is driven by a stationary motorized driving roller, acting on a friction driven drive rail, non-rigidly mounted to the door. A problem with that mechanism is that the supporting elongate guide rail must have a length not less than the sum of the closure element's width and its mensurated translation. US-A-5,040,427 discloses a self-propelled apparatus for linear motion comprising two parallel guide rails, supporting a carriage comprising sliding members fitted in the guide rails for inhibiting lifting. The apparatus further comprises one central stationary non-supporting guide bar for making simultaneously frictionally engaged contact with two driven wheels on the carriage, for moving it with respect to the guide bar. A driving motor mounted on the carriage drives via a rotating shaft the pair of driven wheels. Since in that apparatus two driving contacts with the guide bar are required, extra operating space is necessary, requiring valuable space and numerous extra elements, such as two driven wheels and an extra rotating shaft, increasing the size and cost of the system. Accordingly, it is an object of the present invention to provide a linear motion drive apparatus with a support system wherein the number of elements is reduced, and in preferred embodiments, wherein the carriage is supported at three points and wherein one of the supporting, bearing components is also a point of driving contact. Yet, another object of the present invention is to reduce the length of one of the support rails and reduce manufacturing costs by reducing the number of components in the support system in general. A further object of the present invention is to provide accurate positioning of the supported member with minimal slippage by loading the bearing components with permanent magnets. The above mentioned objects are realized by the specific features according to claim 1. Preferred embodiments of the invention are set out in the dependent claims. According to the present invention, a support for a self-propelled linear motion drive apparatus comprises a fixed base having a carriage member relatively movable thereto along a linear motion axis on two rails mounted to the fixed base and parallel to the linear motion axis. At least one first bearing member is provided for movably supporting the member and is mounted to the member and in rolling contact with a first of the two rails and at least two second bearing members are provided for movably supporting the member being mounted to the movable member and in rolling contact with the second of the two rails such that the first and second bearing members form at least three movable support points of the member. The features and objects of the invention will become apparent in the following description when taken with the accompanying drawings, in which: Figure 1 is an isometric view of a support system according to the present invention used on a carriage of a self-propelled linear drive apparatus; Figure 2 is a bottom view of the carriage of Fig. 1 showing the drive system for the self-propelled carriage; and, Figure 3 is a diagrammatic view of magnetic loading of the carriage of Fig. 1 against a support rail. Referring now to Fig. 1, a linear motion drive apparatus, generally indicated by reference numeral 10, drives a carriage 12 along two spaced guide rails 14, 16 mounted within a stationary housing 17. The carriage 12, generally rectangular in form, has guide rail 16 along longitudinal side wall 18, and guide rail 14 along longitudinal side wall 20 to provide stabilization. The carriage 12 is supported for linear movement along the parallel guide rails 14, 16 by two recirculating ball bearings 22 that allow the carriage 12 to slide with minimal friction. Rail 14 has a V-groove 24 in a top side 26 thereof to accommodate balls 28 of the recirculating ball bearings 22 rolling against the V-grooved rail 14. The bearings 22 are attached to the exterior of the side wall 20 of the carriage 12 and are spaced apart along the V-grooved rail 14 to prevent rotation of the carriage 12 relative to the guide rails 14, 16. Shown in Fig. 2, a drive shaft 30 is supported for rotation by two ball bearings 32 mounted in interior walls 34 of the carriage 12. A "pancake" DC motor 36 is mounted on the carriage 12 to rotate the drive shaft 30. Near one end of the drive shaft 30, a stator motor housing 42 is fixed to an inner portion 44 of the 18, and a side wall rotor 48 is fixed to the drive shaft 30 for rotation therewith. Integral with the same end of the drive shaft 30 is a friction wheel 50 in rolling contact with the flat rail 16 to drive the carriage 12 along the rails 14, 16 upon rotation of the drive shaft 30. Near the center of the drive shaft 30, an inertia wheel 54 is fixed to the drive shaft 30 for rotation therewith to provide rotational inertia and to minimize possible motor torque ripple and transport friction variations. Referring now to Figs. 1 and 3, two permanent magnets 60, 62 are fixed to an outer portion of the side wall 18 of the carriage 12, one on each side of the friction wheel 50. Air gaps 66, 68 are located between each magnet 60, 62 respectively, and the flat rail 16, which can have a ferromagnetic member integral therewith or can be constructed of ferromagnetic material. A magnetic attraction between the magnets 60, 62 and the flat rail 16 urges the friction wheel 50 into frictional engagement with the flat rail 16, providing a firm contact between the friction wheel 50 and the flat rail 16, thereby to minimizing slip. Additionally, frictional contact is maintained between the friction wheel 50 and the flat rail 16 by the gravity load of the carriage 12 when mounted as in Fig. 1, however the gravity load is small compared to the magnetic force and the magnetic loading is sufficient to enable vertical mounting and linear movement in addition to horizontal. It can be seen in Figs. 1 and 3 that the two magnets 60, 62 surrounding the friction wheel 50 are fixed to a steel mounting plate 70 and the steel mounting plate 70 is in turn mounted to the carriage 12 by means of suitable fasteners (not shown). Two smaller steel plates 72, 74 are fixed to the outwardly facing sides of the two magnets 60, 62, respectively, sandwiching each of the two magnets 60, 62 between steel plates. A magnetic circuit is created when the magnets 60, 62 are positioned in the proximity of the ferromagnetic flat rail 16, and the flux lines of the magnetic field circle through the steel plates and the rail around the magnet, creating a force attracting the magnets 60, 62 and the attached carriage 12 to the flat rail 16. Referring now to Fig. 1, on the opposite side wall 20 of the carriage 12, a large magnet 80 is interposed between the two spaced recirculating ball bearings 22. The large magnet 80 is fixed to a steel mounting plate 82 which is fastened to the exterior wall 20 of the carriage 12. The large magnet 80 is also sandwiched by a smaller steel plate 84 mounted to the outer face of the large magnet 80, like the two smaller magnets 60, 62 described above. An air gap (not shown) is located between the large magnet 80 and the V-grooved rail 14, which also has a ferromagnetic portion like the flat rail as described above. The air gap is substantially identical to the air gaps 66, 68 for the magnets 60, 62 shown and described for the flat rail 16 mounting. The large magnet 80 urges the recirculating ball bearings 22 into the V-grooved rail 14. The magnitude of the magnetic load between the magnets 60, 62 and 80 and the rails 14, 16 can be adjusted by changing the width of the air gap by adjusting the mounting position of each magnet with respect to carriage wall 18 or 20. A primary advantage of the configuration of the recirculating ball bearings, the friction drive wheel and the permanent magnets is that the flat rail may be shortened considerably, saving on expensive manufacturing costs. Due to the recirculating ball bearings being mounted at the outer portion of the carriage and spaced apart along the V-grooved rail, the friction wheel and magnets on the other side of the carriage, which are near the center of the carriage, have a shorter linear distance to travel. Another advantage lies in the use of the friction wheel as one of the three support points for mounting the carriage, rather than three recirculating ball bearings, thereby reducing cost. The present invention allows for easy installation and removal of the carriage against the guide rails without any lengthy preloading procedure due to the use of magnets for biasing the carriage and bearing components into the guide rails. The magnets provide a repeatable preload each time the carriage is loaded onto the guide rails, whereas some prior art systems do not allow removal of the carriage from the axis of motion. The low friction rolling contact interface of the carriage with the support and guide rails of the present invention allows smooth uniform carriage motion substantially reducing the drive torque required to move the carriage along the motion axis when compared with the lead screw and friction slide linear drives of the prior art. Modifications are possible within the scope of the appended claims.

Claims: A self-propelled linear motion drive apparatus (10) comprising : a first rail (14) ; a second rail (16) fixed parallelly to said first rail (14) ; a carriage (12) comprising : support means (22, 50) for movably supporting said carriage (12) along said rails (14, 16) ; a drive means (50), arranged for exerting by rotation a drive force on only one (16) of said rails (14, 16) ; is characterised in that said carriage (12) has only one driving contact with said only one rail (16). Apparatus according to claim 1, comprising a motor (36) mechanically coupled to said drive means (50). Apparatus according to claim 2, wherein said drive means (50) is mounted on the shaft (30) of said motor (36). Apparatus according to any of the preceding claims, wherein said only one driving contact is incorporated into one of said support means (22, 50). Apparatus according to any of the preceding claims, wherein the drive means (50) comprises a friction wheel in rolling contact with one of said rails (16), being preferentially a flat rail. Apparatus according claim 5, wherein said friction wheel (50) is loaded by a gravity load or a magnetic loading (60, 62), preferentially by a permanent magnet on said carriage (12). Apparatus according to any of the preceding claims, comprising a magnetic loading (60, 62 ; 80), preferentially a permanent magnet, for biasing at least one of said support means (22, 50) onto said rails (14, 16). Apparatus according to claims 6 or 7, wherein an air gap (66, 68) is located between said permanent magnet (60, 62 ; 80) and a rail (14, 16), said rail : comprising a ferromagnetic portion preferentially by a ferromagnetic member integral therewith ; or, being constructed of ferromagnetic material. Apparatus according to any of the preceding claims, wherein at least one or at least two of said support means (22, 50) are arranged for rolling contact with one of said rails (12, 14). Apparatus according to any of the preceding claims, wherein at least one (14) of said rails (12, 14) includes guide means (24) for guiding said carriage (12) along a linear motion axis. Apparatus according to claim 10, wherein said guide means (24) is a V-groove extending along said rail (14). Apparatus according to any of the preceding claims, wherein at least two support means (22) are formed by recirculating ball bearings. Apparatus according to claim 12, wherein at least one rail (14) has a V-groove (24) in a top side (26) thereof to accommodate balls (28) of said recirculating ball bearings (22). Apparatus according to any of the preceding claims, wherein said carriage (12) is supported at three movable points.

Inventors: BLAKE LAWRENCE S, VIOLA DAVID P, BLAKE, LAWRENCE S., VIOLA, DAVID P.
Applicants: BAYER AG, BAYER CORPORATION
Application year: 1994
Main classification: H02K7
IPC codes: F16C29